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All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Global Geologic Mapping of Io: Preliminary Results

A new global geologic map of Jupiter's volcanic moon, Io is being prepared, with the focus being on completion of a draft map by July 2008. Here initial results of the mapping are reported: a preliminary distribution of material units in terms of areas and a visual representation. Additionally, the mapping hopes to address some of the problems in Io geology. Thus far it has been discovered that Io's surface is dominated by plains material, thought to consist of Io's silicate crust covered by pyroclastic deposits and lava flows of silicate and sulfur-bearing composition. Many plains areas contain flow fields that cannot be mapped separately due to a lack of resolution or modification by alteration processes. Discrete lava flows and flow fields are the next most abundant unit, with bright (sulfur?) flows in greater abundance than dark (silicate?) flows. The source of most of Io's heat flow, the paterae, are the least abundant unit in terms of areal extent.Upon completion of the draft map for peer review, it will be used to investigate several specific questions about the geological evolution of Io that previously could not be well addressed, including: comparison of the areas versus the heights of Ionian mountains to assess their stability and evolution; correlation and comparison of Galileo Near-Infrared Mapping Spectrometer and Photopolarimeter-Radiometer hot spot locations with the mapped location of dark versus bright lava flows and patera floors to assess any variations in the types of sources for Io's active volcanism; and the creation of a global inventory of the areal coverage of dark and bright laval flows to assess the relative importance of sulfur versus silicate volcanism in resurfacing Io, and to assess whether there are regional concentrations of either style of volcanism that may have implications on interior processes.

Williams, David A.↗
NASA NTRS1995

Universities Earth System Scientists Program

This document constitutes the final technical report for the National Aeronautics and Space Administration (NASA) Grant NAGW-3172. This grant was instituted to provide for the conduct of research under the Universities Space Research Association's (USRA's) Universities Earth System Scientist Program (UESSP) for the Office of Mission to Planet Earth (OMTPE) at NASA Headquarters. USRA was tasked with the following requirements in support of the Universities Earth System Scientists Programs: (1) Bring to OMTPE fundamental scientific and technical expertise not currently resident at NASA Headquarters covering the broad spectrum of Earth science disciplines; (2) Conduct basic research in order to help establish the state of the science and technological readiness, related to NASA issues and requirements, for the following, near-term, scientific uncertainties, and data/information needs in the areas of global climate change, clouds and radiative balance, sources and sinks of greenhouse gases and the processes that control them, solid earth, oceans, polar ice sheets, land-surface hydrology, ecological dynamics, biological diversity, and sustainable development; (3) Evaluate the scientific state-of-the-field in key selected areas and to assist in the definition of new research thrusts for missions, including those that would incorporate the long-term strategy of the U.S. Global Change Research Program (USGCRP). This will, in part, be accomplished by study and evaluation of the basic science needs of the community as they are used to drive the development and maintenance of a global-scale observing system, the focused research studies, and the implementation of an integrated program of modeling, prediction, and assessment; and (4) Produce specific recommendations and alternative strategies for OMTPE that can serve as a basis for interagency and national and international policy on issues related to Earth sciences.

Estes, John E.↗
NASA NTRS1988

Gamma ray astrophysics to the year 2000. Report of the NASA Gamma Ray Program Working Group

Important developments in gamma-ray astrophysics up to energies of 100 GeV during the last decade are reviewed. Also, the report seeks to define the major current scientific goals of the field and proposes a vigorous program to pursue them, extending to the year 2000. The goals of gamma-ray astronomy include the study of gamma rays which provide the most direct means of studying many important problems in high energy astrophysics including explosive nucleosynthesis, accelerated particle interactions and sources, and high-energy processes around compact objects. The current research program in gamma-ray astronomy in the U.S. including the space program, balloon program and foreign programs in gamma-ray astronomy is described. The high priority recommendations for future study include an Explorer-class high resolution gamma-ray spectroscopy mission and a Get Away Special cannister (GAS-can) or Scout class multiwavelength experiment for the study of gamma-ray bursts. Continuing programs include an extended Gamma Ray Observatory mission, continuation of the vigorous program of balloon observations of the nearby Supernova 1987A, augmentation of the balloon program to provide for new instruments and rapid scientific results, and continuation of support for theoretical research. Long term recommendations include new space missions using advanced detectors to better study gamma-ray sources, the development of these detectors, continued study for the assembly of large detectors in space, collaboration with the gamma-ray astronomy missions initiated by other countries, and consideration of the Space Station attached payloads for gamma-ray experiments.

Source record↗
NASA NTRS2005

Light-emitting diodes as an illumination source for plants: a review of research at Kennedy Space Center

The provision of sufficient light is a fundamental requirement to support long-term plant growth in space. Several types of electric lamps have been tested to provide radiant energy for plants in this regard, including fluorescent, high-pressure sodium, and metal halide lamps. These lamps vary in terms of spectral quality, which can result in differences in plant growth and morphology. Current lighting research for space-based plant culture is focused on innovative lighting technologies that demonstrate high electrical efficiency and reduced mass and volume. Among the lighting technologies considered for space are light-emitting diodes (LEDs). The combination of red and blue LEDs has proven to be an effective lighting source for several crops, yet the appearance of plants under red and blue lighting is purplish gray, making visual assessment of plant health difficult. Additional green light would make the plant leaves appear green and normal, similar to a natural setting under white light, and may also offer psychological benefits for the crew. The addition of 24% green light (500-600 nm) to red and blue LEDs enhanced the growth of lettuce plants compared with plants grown under cool white fluorescent lamps. Coincidentally, these plants grown under additional green light would have the additional aesthetic appeal of a green appearance.

NASA Discipline Life Support Systems↗
NASA NTRS2015

Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator

The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortex tubes in the center of the impingement region. The causality method based on Lighthill's acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill's stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic FJID models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.

Broadband↗
NASA NTRS2020

Historical and Future Changes in Air Pollutants from CMIP6 Models

Poor air quality is currently responsible for large impacts on human health across the world. In addition, the air pollutants ozone (O3) and particulate matter less than 2.5 µm in diameter (PM2.5) are also radiatively active in the atmosphere and can influence Earth's climate. It is important to understand the effect of air quality and climate mitigation measures over the historical period and in different future scenarios to ascertain any impacts from air pollutants on both climate and human health. The Coupled Model Intercomparison Project Phase 6 (CMIP6) presents an opportunity to analyse the change in air pollutants simulated by the current generation of climate and Earth system models that include a representation of chemistry and aerosols (particulate matter). The shared socio-economic pathways (SSPs) used within CMIP6 encompass a wide range of trajectories in precursor emissions and climate change, allowing for an improved analysis of future changes to air pollutants. Firstly, we conduct an evaluation of the available CMIP6 models against surface observations of O3 and PM2.5. CMIP6 models consistently overestimate observed surface O3 concentrations across most regions and in most seasons by up to 16 ppb, with a large diversity in simulated values over Northern Hemisphere continental regions. Conversely, observed surface PM2.5 concentrations are consistently underestimated in CMIP6 models by up to 10 µg m−3, particularly for the Northern Hemisphere winter months, with the largest model diversity near natural emission source regions. The biases in CMIP6 models when compared to observations of O3 and PM2.5 are similar to those found in previous studies. Over the historical period (1850–2014) large increases in both surface O3 and PM2.5 are simulated by the CMIP6 models across all regions, particularly over the mid to late 20th century, when anthropogenic emissions increase markedly. Large regional historical changes are simulated for both pollutants across East and South Asia with an annual mean increase of up to 40 ppb for O3 and 12 µg m−3 for PM2.5. In future scenarios containing strong air quality and climate mitigation measures (ssp126), annual mean concentrations of air pollutants are substantially reduced across all regions by up to 15 ppb for O3 and 12 µg m−3 for PM2.5. However, for scenarios that encompass weak action on mitigating climate and reducing air pollutant emissions (ssp370), annual mean increases in both surface O3 (up 10 ppb) and PM2.5 (up to 8 µg m−3) are simulated across most regions, although, for regions like North America and Europe small reductions in PM2.5 are simulated due to the regional reduction in precursor emissions in this scenario. A comparison of simulated regional changes in both surface O3 and PM2.5 from individual CMIP6 models highlights important regional differences due to the simulated interaction of aerosols, chemistry, climate and natural emission sources within models. The projection of regional air pollutant concentrations from the latest climate and Earth system models used within CMIP6 shows that the particular future trajectory of climate and air quality mitigation measures could have important consequences for regional air quality, human health and near-term climate. Differences between individual models emphasise the importance of understanding how future Earth system feedbacks influence natural emission sources, e.g. response of biogenic emissions under climate change.

Air pollutants↗
NASA NTRS2013

Characterization of the Reverberation Chamber at the NASA Langley Structural Acoustics Loads and Transmission (SALT) Facility

In 2011 the noise generating capabilities in the reverberation chamber of the Structural Acoustic Loads and Transmission (SALT) facility at NASA Langley Research Center were enhanced with two fiberglass reinforced polyester resin exponential horns, each coupled to Wyle Acoustic Source WAS-3000 airstream modulators. This report describes the characterization of the reverberation chamber in terms of the background noise, diffusivity, sound pressure levels, the reverberation times and the related overall acoustic absorption in the empty chamber and with the acoustic horn(s) installed. The frequency range of interest includes the 80 Hz to 8000 Hz one-third octave bands. Reverberation time and sound pressure level measurements were conducted and standard deviations from the mean were computed. It was concluded that a diffuse field could be produced above the Schroeder frequency in the 400 Hz one-third octave band and higher for all applications. This frequency could be lowered by installing panel diffusers or moving vanes to improve the acoustic modal overlap in the chamber. In the 80 Hz to 400 Hz one-third octave bands a successful measurement will be dependent on the type of measurement, the test configuration, the source and microphone locations and the desired accuracy. It is recommended that qualification measurements endorsed in the International Standards be conducted for each particular application.

Grosveld, Ferdinand W.↗
NASA NTRS1981

A failure mechanism in adaptive arrays

The steady-state behavior of an adaptive array is considered and the degradation of its output SNR in the presence of jammers is analyzed. It is shown that for given incident powers (of jammers and signal), there are geometric configurations of the sources exciting the array for which the SNR degradation is much more pronounced than for other configurations. This result is proved for the case where the thermal noise power of each array receiver is negligible compared to the total power intercepted by the array from each jammer. The result is general, being valid for an array of n arbitrary antennae in an arbitrary three-dimensional configuration. It is stated in terms of linear dependence relationships among the n-dimensional vectors that describe the effects of the sources on the array.

Zohar, S.↗
NASA NTRS2023

Rapidly Evolving Aerosol Emissions Are A Dangerous Omission From Near-Term Climate Risk Assessments

Anthropogenic aerosol emissions are expected to change rapidly over the coming decades, driving strong, spatially complex trends in temperature, hydroclimate, and extreme events both near and far from emission sources. Under-resourced, highly populated regions often bear the brunt of aerosols' climate and air quality effects, amplifying risk through heightened exposure and vulnerability. However, many policy-facing evaluations of near-term climate risk, including those in the latest Intergovernmental Panel on Climate Change assessment report, underrepresent aerosols' complex and regionally diverse climate effects, reducing them to a globally averaged offset to greenhouse gas warming. We argue that this constitutes a major missing element in society's ability to prepare for future climate change. We outline a pathway towards progress and call for greater interaction between the aerosol research, impact modeling, scenario development, and risk assessment communities.

anthropogenic aerosol↗
NASA NTRS1988

Radio flares from AE Aquarii - A low-power analog to Cygnus X-37

The magnetic cataclysmic variable AE Aquarii has been observed at 1.5, 4.9, 15, and 22.5 GHz. The source shows temporal variations in the flux density, often with a flarelike morphology. The flux variations are at times extreme, with values ranging from 1-12 mJy at 15 GHz; the degree of variability increases with frequency. The spectrum shows a variety of short-term behavior, at times increasing as nu, at other times decreasing with nu, and at still others flat. The long-term average of the spectrum increases as nu exp 0.3-0.4. No significant degree of circular polarization was observed. The source properties can be explained as a superposition of flare events in which electrons are accelerated to relativistic energies which then emit synchrotron radiation in discrete, expanding sources. The origin of the flare events may be connected to the disruption of the accretion disk some ditance from the white dwarf primary. The radio emission of AE Aqr shows similarities to the low-level flares from Cygnus X-3.

Bastian, T. S.↗
NASA NTRS1976

Basic limits on protocol information in data communications networks

The paper considers basic limitations on the amount of protocol information that must be transmitted in a data communication network to keep track of source and receiver addresses and of the starting and stopping of messages. Assuming Poisson message arrivals between each communicating source-receiver pair, a lower bound is found on the required protocol information for message. This lower bound is the sum of two terms, one for the message-length information, which depends only on the distribution of message lengths, and the other for the message-start information, which depends only on the product of the source-receiver pair arrival rate and the expected delay for transmitting the message. Two strategies are developed which, in the limit of large numbers of sources and receivers, almost meet the lower bound on protocol information.

Gallager, R. G.↗
NASA NTRS1983

Radiation from a double layer jet

The aerodynamic radiation caused by two acoustic point sources located symmetrically on the sides of a double layer jet which produces a velocity discontinuity was examined, with attention given to the effect on the sound by the stream. Basic equations were defined in terms of wave propagation in the fluid in motion and a Fourier transformation. It was found that the radiation due to a point source on one side of the jet is enhanced by the presence of sound transmitted from the other side. The effect is expressed as a function of the reflection coefficient, wherein the reflections take place at the vortex interfaces separating the fluid in motion from the fluid at rest. The intensity patterns were determined to be kidney-shaped, lung-shaped, and heart-shaped, and characterized by a deep valley in the directivity pattern. The significance of the findings for STOL aircraft ejector thrust augmentation is mentioned.

Dash, R.↗
NASA NTRS1982

Research in atmospheric chemistry and transport

The carbon monoxide cycle was studied by incorporating the known CO sources and sinks in a tracer model which used the winds generated by a general circulation model. The photochemical production and loss terms, which depended on OH radical concentrations, were calculated in an interactive fashion. Comparison of the computed global distribution and seasonal variations of CO with observations was used to yield constraints on the distribution and magnitude of the sources and sinks of CO, and the abundance of OH radicals in the troposphere.

Yung, Y. L.↗
NASA NTRS2012

QuakeSim 2.0

QuakeSim 2.0 improves understanding of earthquake processes by providing modeling tools and integrating model applications and various heterogeneous data sources within a Web services environment. QuakeSim is a multisource, synergistic, data-intensive environment for modeling the behavior of earthquake faults individually, and as part of complex interacting systems. Remotely sensed geodetic data products may be explored, compared with faults and landscape features, mined by pattern analysis applications, and integrated with models and pattern analysis applications in a rich Web-based and visualization environment. Integration of heterogeneous data products with pattern informatics tools enables efficient development of models. Federated database components and visualization tools allow rapid exploration of large datasets, while pattern informatics enables identification of subtle, but important, features in large data sets. QuakeSim is valuable for earthquake investigations and modeling in its current state, and also serves as a prototype and nucleus for broader systems under development. The framework provides access to physics-based simulation tools that model the earthquake cycle and related crustal deformation. Spaceborne GPS and Inter ferometric Synthetic Aperture (InSAR) data provide information on near-term crustal deformation, while paleoseismic geologic data provide longerterm information on earthquake fault processes. These data sources are integrated into QuakeSim's QuakeTables database system, and are accessible by users or various model applications. UAVSAR repeat pass interferometry data products are added to the QuakeTables database, and are available through a browseable map interface or Representational State Transfer (REST) interfaces. Model applications can retrieve data from Quake Tables, or from third-party GPS velocity data services; alternatively, users can manually input parameters into the models. Pattern analysis of GPS and seismicity data has proved useful for mid-term forecasting of earthquakes, and for detecting subtle changes in crustal deformation. The GPS time series analysis has also proved useful as a data-quality tool, enabling the discovery of station anomalies and data processing and distribution errors. Improved visualization tools enable more efficient data exploration and understanding. Tools provide flexibility to science users for exploring data in new ways through download links, but also facilitate standard, intuitive, and routine uses for science users and end users such as emergency responders.

Donnellan, Andrea↗
NASA NTRS1972

Note on the semi-annual effect in the thermosphere

The semi-annual variation in the thermospheric density is discussed in terms of the spatial and temporal variations in the solar heat input. Two heat sources are considered: the solar heat input associated with the semi-annual migration of the sun, and the auroral heat associated with the semi-annual component in magnetic storms. It is shown that the relatively large global component in the semi-annual effect of the total mass density can be explained by the lack of advective loss which otherwise damps the latitude dependent components in the annual and semi-annual variations, and the significant latitude dependence in the semi-annual variations of composition and temperature can be tied to the diffusion process which is induced by the thermospheric circulation.

Volland, H.↗
NASA NTRS1977

Development of a spectral break in the nonthermal emission of AO 0235+164

Results are reported for braod-band photometry of the BL Lac object AO 0235+164 carried out over the spectral range from 0.36 to 3.5 microns in December 1975 and in October and November 1976. It is found that the continuum of this object steepened at visible wavelengths between December 1975 and October 1976, but maintained a relatively constant slope in the near-IR despite a factor-of-ten decrease in flux from the maximum level. Visible-wavelength data are cited which appear to suggest that the steepening of the visible spectrum occurred in less than 300 days, while the near-IR level may have been nearly constant. It is shown that the observed change in the spectral shape of the visible-wavelength continuum cannot be explained in terms of a 'composite' model consisting of an unchanging galaxy and a varying nonthermal source with constant spectral index. Two other general classes of models are considered: intrinsic variability and extrinsic modulation.

Odell, S. L.↗